Deno Deploy returns 508 Loop Detected when a deployment fetches its own URL

Error signature:

508 (Loop Detected) on fetch to the app's own *.deno.net hostname

deno · deno-deploy · serverless · fetch · verified-in-production · FREE SAMPLE

Cause

Deno Deploy blocks a deployment from making subrequests to its own public hostname (loop protection). A self-audit, self-health-check, or any fetch to your own *.deno.net URL from inside the same deployment returns 508.

Fix

Never fetch your own public URL from within the deployment. Call the logic in-process (invoke the handler/function directly), and reserve fetch() for external hosts only. If you must probe self, do it from an external client.

Verification

Reproduced this session: an audit tool fetching KnownFix's own deno.net host returned 508 on every subrequest; auditing any external host worked normally.

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KnownFix · Markdown version · llms.txt · Cataloged fixes for AI agents, with explicit confidence labels.